`81+(-70)+119 +(-30)+1`

`= (81+119)+[(-70)+(-30)] +1`

`= 200+ (-100)+1`

`= 100+1`

`=101`

a) 30 + 192 + 70 = 30 + 70 + 192

= 100 + 192 = 292

b) 50 + 794 + 50 = 50 + 50 + 794

= 100 + 794 = 894

c) 75 + 219 + 25 = 75 + 25 + 219

= 100 + 219 = 319

d) 725 + 199 + 125 = 725 + 125 + 199

= 850 + 199 = 1 049

\(30.\left(-89\right)-68.\left(-30\right)+129.\left(-30\right)\)

\(=\left(-30\right).89-68.\left(-30\right)+129.\left(-30\right)\)

\(=\left(-30\right)\left(89-68+129\right)\)

\(=\left(-30\right).150\)

\(=-4500\)

Ta có:\(\left(\frac{28}{27}-\frac{29}{89}+\frac{30}{89}\right)\left(\frac{1}{3}+\frac{1}{2}-\frac{5}{6}\right)\)

\(=\left(\frac{28}{27}-\frac{29}{89}+\frac{30}{89}\right).\left(\frac{2}{6}+\frac{3}{6}-\frac{5}{6}\right)\)

\(\left(\frac{28}{27}-\frac{29}{89}+\frac{30}{89}\right).0\)

\(=0\)

Đặt A = 28/87 - 29/89 + 30/89 

Ta có : 

   A    . ( 1/3 + 1/2 - 5/6 ) 

= A . ( 2/6 + 3/6 - 5/6 ) 

= A . ( 5/6 - 5/6 ) 

= A . 0 

= 0 

Tham khảo nha !!! Chúc học tốt !!! 

(28/87-29/89+30/89) . (1/3 +1/2-5/6) =0

x.3/10+x.1/4+89=100

x.(3/10+1/4)+89=100

x.11/20+89=100

x.11/20=100-89

x.11/20=11

x=11:11/20

x=20

 X x 3/10 + X x 1/4 + 89 = 100

    X x ( 3/10 + 1/4 ) + 89 = 100

X x 11/20 + 89 = 100

X x 11/20 = 100 - 89

X x 11/20 = 11

X = 11 : 11/20 

X = 20

X x 30 %  +  X x 1/4 + 89 = 100

X x 3/10 + X x 1/4 + 89 = 100

X x ( 3/10 + 1/4 ) + 89 = 100

X x 11/20 + 89 = 100

X x 11/20 = 100 - 89

X x 11/20 = 11

X = 11 : 11/20 

X = 20

326:25=13,04

-1000:25=-40

119:12=9 dư 11

852:25=34,08

286:14=20 dư 6

105:25=4 dư 5

180:60=3

195:25=7 dư 20

786:30=26 dư 6

y*0.3+y*0.25+89=100

y*[0.3+0.25]=100-89=11

y*0.55=11

y=11/0.55

y=20

4^15 x 5^30 = 2^30 x 5^30 = 10^30

\(\frac{11}{1.12}+\frac{11}{12.23}+\frac{11}{23.34}+.......+\frac{11}{78.89}+\frac{11}{98.100}\)

\(=1-\frac{1}{12}+\frac{1}{12}-\frac{1}{23}+....+\frac{1}{89}-\frac{1}{100}\)

\(=1-\frac{1}{100}\)

\(=\frac{99}{100}\)